fix(scripts): changelog_housekeeping misses two boundary footers

[doobidoo]

Context

During PR #716 (docs: rotate changelog — archive 35 versions), Gemini review caught two hardcoded version-boundary strings that `scripts/maintenance/changelog_housekeeping.py` should have rewritten but didn't:

1. README.md "Full version history" footer:
   ```markdown
   Full version history: CHANGELOG.md | Older versions (v10.22.0 and earlier) | All Releases
   ```

2. docs/archive/CHANGELOG-HISTORIC.md header:
   ```markdown
   Older changelog entries for MCP Memory Service (v10.24.0 and earlier).
   ```

Both footers still referenced ancient boundaries (v10.22, v10.24) from earlier archivals. They had to be patched manually.

Why the script missed them

`update_header_range()` in the script only matches two patterns:

• `Recent releases for MCP Memory Service (vX.Y.Z and later)`
• `Versions vX.Y.Z and earlier`

The two footers above are in different formats:

• README: markdown-link text `Older versions (vX.Y.Z and earlier)` (not bolded)
• HISTORIC: plain prose `Older changelog entries for MCP Memory Service (vX.Y.Z and earlier).`

Proposed fix

Extend `update_header_range()` (or add a sibling function `update_all_boundaries()`) to also match:

• `\[Older versions \(v[\d.]+ and earlier\)\]` → rewrite the version
• `Older changelog entries for MCP Memory Service \(v[\d.]+ and earlier\)\.` → rewrite the version

Both should be replaced with the `newest_archived` version the script already computes.

Definition of Done

• Both patterns rewritten by the script on every rotation
• Dry-run output mentions footer updates explicitly
• Test with synthetic README + HISTORIC containing various boundary formats
• Next rotation doesn't need manual Gemini follow-up for these

Related

• PR docs: rotate changelog — archive 35 versions, trim README #716 (rotation that surfaced this)
• PR chore: add automated changelog housekeeping workflow #578 (script origin)